Centrifugal clutch

ABSTRACT

A centrifugal clutch  200  includes a first drive plate  210  rotationally driven directly by a driving force of an engine and a second drive plate  220  frictionally in contact with the first drive plate  210 . The first drive plate  210  includes a bulging body  215  on a supporting portion  214  bulging toward the second drive plate  220 . The second drive plate  220  is rotationally driven together with the first drive plate  210  while allowing rotational displacement relative to the first drive plate and includes clutch weights  230 . The bulging body  215  is made of a cylindrical roller. The clutch weight  230  is formed with a driven portion  232 . The driven portion  232  has a pressing body  232   a  in contact with the bulging body  215 . The pressing body  232   a  obliquely extends rearwardly and outwardly in a rotational drive direction of the first drive plate  210.

TECHNICAL FIELD

The present invention relates to a centrifugal clutch, which cuts offtransmission of a rotational driving force to a driven side until arotational speed of an engine reaches a predetermined value, andtransmits the rotational driving force to the driven side when therotational speed of the engine reaches the predetermined value.

BACKGROUND ART

Conventionally, the centrifugal clutch is used for a motorcycle, a brushcutter, and the like. The centrifugal clutch transmits the rotationaldriving force to the driven side when the rotational speed of the enginereaches the predetermined value. For example, in the centrifugal clutchdisclosed in Patent Document 1, as the rotational speed of the engineincreases, a clutch weight is gradually displaced to a side of a clutchouter and makes frictional contact. Further, in the centrifugal clutchdisclosed in Patent Document 2, a columnar roller rides on a cam-shapedprotrusion rotationally driven by a driving force of the engine, so thatclutch shoes provided on an outer side of the roller press the clutchouter to bring the clutch into a connected state.

CITATION LIST Patent Literature

Patent Document 1: JP-A-2006-038124

Patent Document 2: JP-UM-B-42-015451

However, in the centrifugal clutch described in the above-describedPatent Document 1, the clutch weight gradually makes frictional contactwith the clutch outer as the rotational speed of the engine increases.Therefore, since time until the clutch enters the connected statebecomes longer, there is a problem that fuel economy decreases. On theother hand, in the centrifugal clutch described in Patent Document 2,immediately after the cam-shaped protrusion rotates, the roller rides onthe cam-shaped protrusion, and the clutch enters the connected state.Therefore, since the driven side suddenly operates, there has been aproblem that it is difficult for an operator to handle.

The present invention has been made to address the above problems. Anobject of the present invention is to provide a centrifugal clutchcapable of quickly establishing a connected state while preventingsudden startup on a driven side.

SUMMARY OF THE INVENTION

In order to achieve the above object, the present invention is acentrifugal clutch including a first drive plate rotationally driventogether with a driven pulley by receiving a driving force of an engine,a second drive plate disposed outside the first drive plate andcontacting the first drive plate with a frictional force capable ofbeing rotationally driven together with the first drive plate whileallowing rotational displacement relative to the first drive plate, aclutch weight movably mounted on the second drive plate, displacedoutwardly to the second drive plate by a centrifugal force due torotation drive of the second drive plate, and having a clutch shoe on asurface outside thereof, a clutch outer having a cylindrical surface infrictional contact with the clutch shoe displaced outwardly to thesecond drive plate, a bulging body formed to bulge outwardly from anouter circumferential portion of the first drive plate, and a pressingbody provided on the clutch weight and pressed against the bulging body,wherein at least one of the bulging body and the pressing body is formedto extend rearwardly in a rotational drive direction of the first driveplate and outwardly to the first drive plate.

According to a feature of the present invention configured as describedabove, in the centrifugal clutch, after the first drive plate startsrotation drive, the clutch shoes contact the clutch outer. Thus, whenthe second drive plate is displaced rearward in the rotational drivedirection with respect to the first drive plate, the pressing body rideson the bulging body. Thus, the clutch shoes rapidly press the clutchouter. That is, time until the clutch shoes contact the clutch outer issecured from when the first drive plate starts rotation drive until whenthe centrifugal clutch enters the connected state. Further, when theclutch shoes contact the clutch outer, the centrifugal clutch rapidlyshifts to the connected state. As a result, the centrifugal clutch canquickly enter the connected state while preventing sudden startup on thedriven side.

Further, in the centrifugal clutch according to the present invention,since the pressing body rides on the bulging body, the clutch shoes arestrongly pressed against the clutch outer. Therefore, the rotationaldriving force from the engine can be transmitted with a clutch weightlighter than a conventional centrifugal clutch even when the rotationalspeed is the same as that of the conventional centrifugal clutch. Thatis, according to the centrifugal clutch of the present invention, it ispossible to reduce weight of the clutch weight. Therefore, it ispossible to prevent occurrence of judder at the time of connecting theclutch. Further, it is possible to realize simplification,compactification and cost reduction of a structure of the centrifugalclutch. This means that when the weight of the clutch weight is the sameas the conventional centrifugal clutch, it is possible to increase thedriving force which can be transmitted by the centrifugal clutch. In thecentrifugal clutch according to the present invention, it is alsopossible to appropriately adjust the time until the clutch enters theconnected state by adjusting magnitude of the frictional force at thecontact surface between the first drive plate and the second driveplate.

Another feature of the present invention resides in that, in thecentrifugal clutch, the pressing body is constituted by a flat surface,and the bulging body is constituted by a curved surface partiallycontacting the pressing body.

According to another feature of the present invention configured asdescribed above, in the centrifugal clutch, the bulging body is formedin a curved surface shape, and the pressing body is formed in a flatshape. Therefore, as compared with a case where both the bulging bodyand the pressing body make surface contact, frictional resistance ismore suppressed, and the clutch weight is more easily rotationallydisplaced. Further, as compared with a case where the pressing body isformed in a curved surface shape, it is easier to form the bulging bodyand the pressing body.

Further, another feature of the present invention resides in that, inthe centrifugal clutch, the bulging body is made of a roller rotatablyprovided rearward in the rotational drive direction of the first driveplate.

According to another feature of the present invention configured asdescribed above, in the centrifugal clutch, the bulging body is made ofthe roller rotatably provided rearward in the rotational drive directionof the first drive plate. Therefore, by rotation of the bulging bodyagainst which the pressing body is pressed, it is possible to preventincrease in frictional resistance and damage due to wear due to frictionsliding between the bulging body and the pressing body.

Further, another feature of the present invention resides in that, inthe centrifugal clutch, at least one of an outer circumferential portionand an inner circumferential portion of the second drive plate has abent portion bent with respect to a plate surface.

According to another feature of the present invention configured asdescribed above, in the centrifugal clutch, at least one of the outercircumferential portion and the inner circumferential portion of thesecond drive plate has the bent portion bent with respect to the platesurface. Therefore, it is possible to increase rigidity of the seconddrive plate, which supports the clutch weight and transmits the drivingforce.

Further, another feature of the present invention resides in that, inthe centrifugal clutch, the pressing body is made of a material moreeasily worn than the bulging body. In this case, the pressing body canbe made of, for example, a material having lower hardness than thebulging body. Specifically, for example, the pressing body can be madeof zinc material, and the bulging body can be made of carbon steel, ironbased sintered material or the like. Further, for example, the pressingbody and the bulging body can be made of the same material, and byapplying a surface hardening treatment such as heat treatment or coatingto the bulging member, higher wear resistance than the pressing body canbe obtained.

According to another feature of the present invention configured asdescribed above, in the centrifugal clutch, the pressing body is made ofa material more easily worn than the bulging body. Therefore, thepressing body wears more than the bulging body. In this case, thepressing body is formed in the clutch weight including the clutch shoe.Therefore, the pressing body is renewed by replacing the clutch weightdue to wear of the clutch shoe. That is, in the centrifugal clutch, byexchanging the clutch weigh due to wear of the clutch shoe, the pressingbody can also be replaced with a new one at the same time, so thatmaintenance burden can be reduced.

Further, another feature of the present invention resides in that, inthe centrifugal clutch, at least one of two contact surfaces where thefirst drive plate and the second drive plate are in contact with eachother is subjected to surface treatment to maintain slidability. In thiscase, various coating processes which can improve the wear resistancecan be employed as the surface treatment, in addition to the heattreatment such as nitriding treatment and carburizing treatment.

According to another feature of the present invention configured asdescribed above, in the centrifugal clutch, at least one of two contactsurfaces where the first drive plate and the second drive plate are incontact with each other is subjected to surface treatment to maintainslidability. Therefore, it is possible to improve durability so that themaintenance burden can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan sectional view schematically showing a configuration ofa power transmission mechanism including a centrifugal clutch accordingto the present invention;

FIG. 2 is a side view of the centrifugal clutch taken along a line 2-2shown in FIG. 1;

FIGS. 3A and 3B show appearance configurations of a first drive plateand a second drive plate in the centrifugal clutches shown in FIGS. 1and 2, wherein FIG. 3A is a perspective view showing a state beforeassembling the first drive plate and the second drive plate, and FIG. 3Bis a perspective view showing a state where the first drive plate andthe second drive plate are assembled;

FIGS. 4A to 4D show appearance configuration of the bulging body in thecentrifugal clutch shown in FIG. 1 and FIG. 2 and an assembled state ofthe bulging body on the first drive plate, wherein FIG. 4A is aperspective view showing a state before assembling the bulging body fromoutside the first drive plate, FIG. 4B is a perspective view showing thestate before assembling the bulging body from inside the first driveplate, FIG. 4C is a perspective view showing a state where the bulgingbody is assembled from outside the first drive plate, and FIG. 4D is aperspective view showing the state where the bulging body is assembledfrom inside the first drive plate;

FIG. 5 is a partially enlarged view showing the bulging body and thepressing body in the centrifugal clutch shown in FIG. 2 in a state wherethe clutch shoes are not in contact with the clutch outer;

FIG. 6 is a partially enlarged view showing a contact state between thebulging body and the pressing body in a connected state in contact withthe clutch outer in a state where the clutch shoe in the centrifugalclutch shown in FIG. 5 is not worn, and showing a state where thebulging body pushes up the pressing body;

FIG. 7 is a partially enlarged view showing a state where a pushed-upstate of the pressing body by the bulging body in the centrifugal clutchshown in FIG. 6 is canceled;

FIG. 8 is a partially enlarged view showing the contact state betweenthe bulging body and the pressing body in the connected state in contactwith the clutch outer in a state where the clutch shoe in thecentrifugal clutch shown in FIG. 5 is worn by about 1 mm;

FIG. 9 is a partially enlarged view showing the contact state betweenthe bulging body and the pressing body in the connected state in contactwith the clutch outer in a state where the clutch shoe in thecentrifugal clutch shown in FIG. 5 is worn by about 2 mm;

FIG. 10 is a plan sectional view schematically showing a configurationof a power transmission mechanism including the centrifugal clutchaccording to a modification of the present invention;

FIGS. 11A to 11D show appearance configuration of the bulging body inthe centrifugal clutch shown in FIG. 10 and an assembled state of thebulging body on the first drive plate, wherein FIG. 11A is a perspectiveview showing a state before assembling the bulging body from outside thefirst drive plate, FIG. 11B is a perspective view showing the statebefore assembling the bulging body from inside the first drive plate,FIG. 11C is a perspective view showing a state where the bulging body isassembled from outside the first drive plate, and FIG. 11D is aperspective view showing the state where the bulging body is assembledfrom inside the first drive plate;

FIG. 12 is a partially enlarged view corresponding to FIG. 5 taken alonga line 2-2 in FIG. 10, showing the bulging body and the pressing body inthe centrifugal clutch in a disconnected state where the clutch shoes donot contact the clutch outer; and

FIG. 13 is a partially enlarged view corresponding to FIG. 6 taken alongthe line 2-2 in FIG. 10, showing the contact state between the bulgingbody and the pressing body in the connected state in contact with theclutch outer in a state where the clutch shoe in the centrifugal clutchis not worn.

DESCRIPTION OF EMBODIMENTS

An embodiment of a centrifugal clutch according to the present inventionwill be described with reference to the drawings below. FIG. 1 is a plansectional view schematically showing a configuration of a powertransmission mechanism 100 including a centrifugal clutch 200 accordingto the present invention. FIG. 2 is a side view of the centrifugalclutch 200 taken along a line 2-2 shown in FIG. 1. The powertransmission mechanism 100 including the centrifugal clutch 200 is amechanical device provided between an engine and a rear wheel which is adriving wheel, mainly in a motorcycle vehicle such as a scooter, andtransmits or cuts off a rotational driving force to the rear wheel whileautomatically changing a reduction ratio with respect to the number ofrevolutions of the engine.

(Configuration of Centrifugal Clutch 200)

The power transmission mechanism 100 mainly includes a transmission 101and the centrifugal clutch 200. The transmission 101 is a mechanicaldevice which decelerates the rotational driving force from the engine(not shown) in a stepless manner and transmits it to the centrifugalclutch 200. The transmission 101 mainly includes a drive pulley 110, aV-belt 120, and a driven pulley 130. Among these, the drive pulley 110is provided on a crankshaft 111 extending from the engine and is amechanical device directly driven to rotate by the rotational drivingforce of the engine. The drive pulley 110 mainly includes a fixed driveplate 112 and a movable drive plate 113.

The fixed drive plate 112 is a component which is rotationally driventogether with the movable drive plate 113 while holding the V-belt 120therebetween. The fixed drive plate 112 is configured by forming a metalmaterial into a conical cylindrical shape. The fixed drive plate 112 isfixedly mounted on the crankshaft 111 in a state where a convex sidesurface thereof faces toward the movable drive plate 113 (engine). Thatis, the fixed drive plate 112 is always rotationally driven togetherwith the crankshaft 111. Further, a plurality of radiating fins 112 aare radially provided on a concave side surface of the fixed drive plate112.

The movable drive plate 113 is a component which is rotationally driventogether with the fixed drive plate 112 while holding the V-belt 120therebetween. The movable drive plate 113 is configured by forming ametal material into a conical cylindrical shape. The movable drive plate113 is mounted on the crankshaft 111 in a direction where a convex sidesurface thereof faces the fixed drive plate 112. In this case, themovable drive plate 113 is mounted on a sleeve bearing 114 fixedlyfitted into the crankshaft 111 via an impregnated bush. The movabledrive plate 113 is slidably mounted on the sleeve bearing 114 in anaxial direction and a circumferential direction thereof.

On the other hand, a plurality of roller weights 115 are provided in astate pressed by a ramp plate 116 on a concave side surface of themovable drive plate 113. The roller weight 115 is a component forpressing the movable drive plate 113 toward the fixed drive plate 112 incooperation with the ramp plate 116 by being displaced outwardly in aradial direction in accordance with increase in rotational speed of themovable drive plate 113. The roller weight 115 is configured by forminga metal material into a cylindrical shape. Further, the ramp plate 116is a component for pressing the roller weight 115 toward the movabledrive plate 113. The ramp plate 116 is formed by bending a metal platetoward the movable drive plate 113.

The V-belt 120 is a component for transmitting the rotational drivingforce of the drive pulley 110 to the driven pulley 130. The V-belt 120is formed in an endless ring shape made of a core wire covered with aresin material. The V-belt 120 is disposed between the fixed drive plate112 and the movable drive plate 113 and between a fixed driven plate 131and a movable driven plate 134 in the driven pulley 130, and is bridgedbetween the drive pulley 110 and the driven pulley 130.

The driven pulley 130 is a mechanical device rotationally driven by therotational driving force from the engine, which is transmitted via thedrive pulley 110 and the V-belt 120. The driven pulley 130 mainlyincludes the fixed driven plate 131 and the movable driven plate 134.

The fixed driven plate 131 is a component which is rotationally driventogether with the movable driven plate 134 while holding the V-belt 120therebetween. The fixed driven plate 131 is configured by forming ametal material into a conical cylindrical shape. The fixed driven plate131 is fixedly mounted on a driven sleeve 132 in a state where a convexside surface thereof faces toward the movable driven plate 134.

The driven sleeve 132 is a metallic cylindrical component which isrotationally driven together with the fixed driven plate 131. The drivensleeve 132 is mounted on a drive shaft 133 to be relatively rotatablevia a bearing. The drive shaft 133 is a metal rotary shaft body fordriving the rear wheel of the motorcycle vehicle on which the powertransmission mechanism 100 is mounted via a transmission (not shown). Inthis case, the rear wheel of the motorcycle vehicle is mounted on oneend (right end in the drawing) of the drive shaft 133.

The movable driven plate 134 is a component which is rotationally driventogether with the fixed driven plate 131 while holding the V-belt 120therebetween. The movable driven plate 134 is configured by forming ametal material into a conical cylindrical shape. The movable drivenplate 134 is fitted into the driven sleeve 132 to be axially slidable ina direction where a convex side surface thereof faces the fixed drivenplate 131.

On the other hand, on a concave side surface of the movable driven plate134, a torque spring 135 is provided between the concave side surfaceand a first drive plate 210 of the centrifugal clutch 200. The torquespring 135 is a coil spring which elastically presses the movable drivenplate 134 toward the fixed driven plate 131. That is, the transmission101 shifts a rotational speed of the engine steplessly using a magnituderelation between a diameter sandwiching the V-belt 120 defined by adistance between the fixed drive plate 112 and the movable drive plate113, and a diameter sandwiching the V-belt 120 defined by a distancebetween the fixed driven plate 131 and the movable driven plate 134. Thecentrifugal clutch 200 is provided on a distal end side of the drivensleeve 132 and on a distal end side of the drive shaft 133.

The centrifugal clutch 200 is a mechanical device which transmits orcuts off the rotational driving force of the engine, which istransmitted via the transmission 101, to the drive shaft 133. Thecentrifugal clutch 200 mainly includes the first drive plate 210, asecond drive plate 220, clutch weights 230, and a clutch outer 240.

The first drive plate 210 is a component rotationally driven togetherwith the driven sleeve 132, and is configured by forming a metalmaterial into a bottomed cylindrical shape. More specifically, as shownin FIGS. 3A and 3B, in the first drive plate 210, a through-hole 212through which the driven sleeve 132 passes is formed in a centralportion of a flat bottom portion 211. Further, three supporting portions214 are provided at equal intervals in a circumferential direction at adistal end of a cylinder portion 213 erected around the bottom portion211.

The supporting portion 214 is a portion hooked on an innercircumferential portion of the second drive plate 220 and is a portionfor supporting a bulging body 215. The supporting portion 214 is formedso as to bulge radially outward from the distal end of the cylinderportion 213. A through-hole 214 a is formed in the supporting portion214. A holding pin 216 passing through the bulging body 215 is fittedinto the through-hole 214 a.

The bulging body 215 is a component for pressing the clutch weight 230described later toward the clutch outer 240. The bulging body 215 isconfigured by forming a metal material (for example, carbon steel andiron based sintered material) into a cylindrical shape. Morespecifically, as shown in FIGS. 4A to 4D, in the bulging body 215, athrough-hole 215 a thereof through which the holding pin 216 passes isformed in a central portion of a columnar body. In this case, thethrough-hole 215 a is formed to have an inner diameter rotatable andslidable with respect to the holding pin 216, that is, a dimensionaltolerance which is a so-called clearance fit with respect to the holdingpin 216.

The holding pin 216 is a rod-shaped member for mounting the bulging body215 on the supporting portion 214 in a rotatable state. The holding pin216 is formed in such a shape that a distal end portion of a metal rodbody thereof projects like a flange. In this case, the holding pin 216is formed to have an outer diameter rotatable and slidable with respectto the through-hole 214 a, that is, a dimension tolerance which is theso-called clearance fit with respect to the through-hole 214 a. In FIG.3B, illustration of the bulging body 215 and the holding pin 216 isomitted.

In the first drive plate 210, the cylinder portion 213 is fitted into athrough-hole 222 of the second drive plate 220 illustration of Thesecond drive plate 220 is a component which is rotationally driventogether with the first drive plate 210 while allowing relativerotational displacement. The second drive plate 220 is configured byforming a metal material into a flat ring shape. More specifically, inthe second drive plate 220, the through-hole 222 into which the cylinderportion 213 of the first drive plate 210 is slidably fitted is formed ina central portion of a plate-like ring plate 221. Further, three fulcrumpins 223 are provided in an upright state at equal intervals in acircumferential direction on the ring plate 221. The fulcrum pin 223 isa component for rotatably supporting the clutch weight 230, and is madeof a metal rod. Further, a bent portion 224 bent at a right angle to aplate surface of the ring plate 221 is formed in each of the innercircumferential portion and an outer circumferential portion of thesecond drive plate 220.

The clutch weight 230 is a component for transmitting or cutting off therotational driving force from the engine to the drive shaft 133 bycontacting or separating from the clutch outer 240 via a clutch shoe 233according to the rotational speed of the second drive plate 220. Theclutch weight 230 is configured by forming a metal material (forexample, zinc material) in a curved shape extending in a circumferentialdirection of the second drive plate 220. One end of the clutch weight230 is rotatably supported by the fulcrum pin 223. In this state, theclutch weights 230 are pulled such that the mutually adjacent clutchweights 230 in the three clutch weights 230 are connected to each otherby a connecting spring 231 and are rotated inward of the second driveplate 220. In FIG. 2, for easy understanding of configuration of theclutch weights 230, a part of the two clutch weights 230 out of thethree clutch weights 230 is shown broken in different thicknessdirection faces.

Each driven portion 232 recessed concavely is formed in a portion facingthe bulging body 215 of the first drive plate 210 on an innercircumferential surface of each clutch weight 230, more specifically, ona back surface of a lower surface (back side surface in the drawing) ofthe connecting spring 231. The driven portion 232 is a portion forcooperating with the bulging body 215 to displace the clutch weight 230toward the clutch outer 240. The driven portion 232 is configured tohave a pressing body 232 a which is a flat inclined surface. Morespecifically, the pressing body 232 a is formed to obliquely extendrearwardly and outwardly in a rotational drive direction of the firstdrive plate 210.

In this driven portion 232, thickness of the pressing body 232 a isformed thicker than thickness of the bulging body 215. Further, thepressing body 232 a is in contact with an outer circumferential surfaceof the bulging body 215. Further, in the driven portion 232, thepressing body 232 a is made of a material which is more easily worn thanthe bulging body 215. In the present embodiment, the driven portion 232is made of the same metal material (for example, zinc material) as theclutch weight 230. Further, in the driven portion 232, a portion whichis deeper than the pressing body 232 a is cut out in an arc shape. Thus,a space for rotation of the bulging body 215 is secured.

On the other hand, the clutch shoes 233 are respectively provided onouter circumferential surfaces of the clutch weights 230. The clutchshoe 233 is a component for increasing frictional force against an innercircumferential surface of the clutch outer 240, and is configured byforming friction material in a plate shape extending in an arc shape.

The clutch outer 240 is a component which is rotationally driventogether with the drive shaft 133. The clutch outer 240 is configured byforming a metal material into a cup shape covering the outercircumferential surface of the clutch weight 230 from the first driveplate 210. That is, the clutch outer 240 is configured to have acylindrical surface 241 which frictionally contacts the clutch shoe 233of the clutch weight 230, which is displaced toward an outercircumference of the second drive plate 220.

(Operation of Centrifugal Clutch 200)

Next, an operation of the centrifugal clutch 200 configured as describedabove will be described. The centrifugal clutch 200 constitutes a partof the power transmission mechanism 100 disposed between the engine andthe rear wheel as the driving wheel in the motorcycle vehicle (forexample, a scooter) and functions as the part of the power transmissionmechanism 100. First, as shown in FIG. 5, when the engine is in anidling state, the centrifugal clutch 200 cuts off transmission of thedriving force between the engine and the drive shaft 133. Specifically,in the centrifugal clutch 200, the first drive plate 210 and the seconddrive plate 220 pressed to the first drive plate 210 via the bulgingbody 215 and the pressing body 232 a are rotationally driven togetherdue to the rotational driving force of the engine transmitted via thetransmission 101, and further the clutch weight 230 is rotationallydriven. In FIG. 5, the connecting spring 231 is omitted in order toclarify a contact state between the bulging body 215 and the drivenportion 232.

However, in this case, in the centrifugal clutch 200, since acentrifugal force acting on the clutch weight 230 is smaller thanelastic force (tensile force) of the connecting spring 231, the clutchshoe 233 does not contact the cylindrical surface 241 of the clutchouter 240, so that the rotational driving force of the engine is nottransmitted to the drive shaft 133. In this case, the bulging body 215and the driven portion 232 maintain a state where the pressing body 232a is pressed to contact a roller surface of the bulging body 215 by theelastic force (tensile force) of the connecting spring 231.

On the other hand, the centrifugal clutch 200 transmits the rotationaldriving force of the engine to the drive shaft 133 in accordance withincrease in the rotational speed of the engine by a driver's acceleratoroperation in the motorcycle vehicle. Specifically, as shown in FIG. 6,in the centrifugal clutch 200, as the rotational speed of the engineincreases, the centrifugal force acting on the clutch weight 230 isgreater than the elastic force (tensile force) of the connecting spring231. Thus, the clutch weight 230 rotates around the fulcrum pin 223 andis displaced radially outwardly. That is, in the centrifugal clutch 200,as the rotational speed of the engine increases, the clutch weight 230is rotationally displaced toward the cylindrical surface 241 of theclutch outer 240 while resisting the elastic force (tensile force) ofthe connecting spring 231. As a result, the clutch shoe 233 contacts thecylindrical surface 241. In FIG. 6, the connecting spring 231 is omittedin order to clarify the contact state between the bulging body 215 andthe driven portion 232. Further, in FIGS. 2 and 6, the rotational drivedirection of the first drive plate 210, the second drive plate 220, theclutch outer 240, and the bulging body 215 in the centrifugal clutch 200is indicated by a dashed arrow.

When the clutch shoe 233 contacts the cylindrical surface 241, theclutch weight 230 receives a reaction force in a direction opposite tothe rotational drive direction via the clutch shoe 233. Therefore, thesecond drive plate 220 is relatively displaced in a direction oppositeto the rotational drive direction of the first drive plate 210 by thereaction force received by the clutch weight 230. Thus, the clutchweight 230 supported by the second drive plate 220 is relativelydisplaced in the direction opposite to the rotational drive direction ofthe first drive plate 210. Therefore, the pressing body 232 a of thedriven portion 232 is pressed against the bulging body 215.

In this case, since the bulging body 215 is rotatably supported withrespect to the supporting portion 214 of the first drive plate 210 andthe holding pin 216, it rotates in a counterclockwise direction as shownby pressing by the pressing body 232 a. Thus, in the clutch weight 230,the pressing body 232 a is pressed toward the clutch outer 240 on aradially outer side according to rotational displacement of the bulgingbody 215. Further, the clutch shoe 233 is pressed against thecylindrical surface 241. As a result, after the clutch shoe 233 contactsthe cylindrical surface 241 of the clutch outer 240, the clutch shoe 233is pressed against the cylindrical surface 241 in an extremely shorttime (in other words, instantaneously). Thus, the centrifugal clutch 200enters a connected state where the rotational driving force of theengine is completely transmitted to the drive shaft 133.

In the centrifugal clutch 200 in the connected state, since a statewhere the pressing body 232 a of the driven portion 232 is pressedagainst the bulging body 215 is maintained, the first drive plate 210and the second drive plate 220 are rotationally driven together.Further, since a state where the clutch shoe 233 is pressed against thecylindrical surface 241 of the clutch outer 240 is maintained, thesecond drive plate 220 and the clutch outer 240 are rotationally driventogether. Thus, the motorcycle vehicle can run since the rear wheel isrotationally driven by the rotational driving force of the engine. Inthis case, although the second drive plate 220 is formed in a ringshape, the second drive plate 220 has high rigidity due to the bentportions 224 formed on the inner circumferential portion and the outercircumferential portion, so that the rotational driving force can beaccurately transmitted.

On the other hand, when the rotational speed of the engine decreases,the centrifugal clutch 200 cuts off transmission of the rotationaldriving force of the engine to the drive shaft 133. Specifically, incentrifugal clutch 200, the centrifugal force acting on the clutchweight 230 is smaller than the elastic force (tensile force) ofconnecting spring 231 as the engine speed decreases. Thus, the clutchweight 230 is rotationally displaced radially inwardly around thefulcrum pin 223.

In this case, as shown in FIG. 7, the bulging body 215 against which thepressing body 232 a is pressed is rotationally displaced clockwise inthe drawing due to the elastic force (tensile force) of the connectingspring 231. Therefore, the second drive plate 220 is rotationallydisplaced forward in a rotation direction of the first drive plate 210relatively with respect to the first drive plate 210. Thus, the seconddrive plate 220 returns to an original position (a position in theidling state) with respect to the first drive plate 210. That is, thecentrifugal clutch 200 enters a disconnected state, where the clutchshoes 233 are not in contact with the clutch outer 240 and therotational driving force is not transmitted. In FIG. 7, the connectingspring 231 is omitted in order to clarify the contact state between thebulging body 215 and the driven portion 232. Further, in FIG. 7, therotational drive direction of the first drive plate 210, the seconddrive plate 220, the clutch outer 240 and the bulging body 215 in thecentrifugal clutch 200 is indicated by a dashed arrow.

Even when thickness of the clutch shoe 233 decreases due to wear, thecentrifugal clutch 200 can enter the connected state by quickly pressingthe clutch shoe 233 against the cylindrical surface 241 of the clutchouter 240. That is, as shown in FIGS. 8 and 9, in the centrifugal clutch200, the bulging body 215 is rotatably mounted on the supporting portion214 and the holding pin 216. Therefore, even when the clutch shoe 233 isworn, an amount of rotational displacement of the bulging body 215increases by an amount corresponding to this wear amount. Therefore,pressing force of the clutch shoe 233 against the cylindrical surface241 of the clutch outer 240 is maintained. In FIGS. 8 and 9, theconnecting spring 231 is omitted in order to clarify the contact statebetween the bulging body 215 and the driven portion 232. Further, inFIGS. 8 and 9, the rotational drive direction of the first drive plate210, the second drive plate 220, the clutch outer 240, and the bulgingbody 215 in the centrifugal clutch 200 is indicated by a dashed arrow.

As can be understood from the above description of the operation,according to the above embodiment, in the centrifugal clutch 200, afterthe first drive plate 210 starts rotation drive, the clutch shoes 233contact the clutch outer 240. Thus, when the second drive plate 220 isdisplaced rearward in the rotational drive direction with respect to thefirst drive plate 210, the driven portion 232 rides on the bulging body215. Thus, the clutch shoes 233 rapidly press the clutch outer 240. Thatis, the time until the clutch shoes 233 contact the clutch outer 240 issecured from when the first drive plate 210 starts rotation drive untilwhen the centrifugal clutch 200 enters the connected state. Further,when the clutch shoes 233 contact the clutch outer 240, the centrifugalclutch 200 rapidly enters the connected state. As a result, thecentrifugal clutch 200 can quickly enter the connected state whilepreventing sudden startup on the driven side such as the driving wheel.

Further, embodiments of the present invention are not limited to theabove embodiment. The above embodiment can be variously modified withoutdeparting from an object of the present invention. In each of thefollowing modifications, the same reference numerals are denoted to thesame constituent parts as in the above embodiment, and the descriptionthereof will be omitted.

For example, in the above embodiment, the bulging body 215 is rotatablymounted on the supporting portion 214 of the first drive plate 210.However, the bulging body 215 may be fixedly mounted on the supportingportion 214 of the first drive plate 210, or integrally formed of thesame material with the first drive plate 210. When the bulging body 215is integrally formed of the same material with the first drive plate210, the bulging body 215 is preferably formed of a curved surfaceincluding a circular arc surface of one, two or more curvatures in arange where the pressing body 232 a slides. Further, the bulging body215 and the driven portion 232 respectively provided in the first driveplate 210 and the clutch weight 230 may be provided at least one each,that is, at least one pair.

Further, in the above embodiment, the bulging body 215 is made of aroller. However, the bulging body 215 may be formed to bulge outwardlyfrom an outer circumferential portion of the first drive plate 210, andmay be formed in a shape such that the clutch weight 230 is pressed outoutwardly via the pressing body 232 a. That is, at least one of thebulging body 215 and the pressing body 232 a may be formed to extendrearward in the rotational drive direction of the first drive plate 210and outwardly to the first drive plate 210. In this case, in the bulgingbody 215 and the pressing body 232 a, a portion extending rearward inthe rotational drive direction of the first drive plate 210 andoutwardly to the first drive plate 210 may be formed in the whole or apart of the bulging body 215 and the pressing body 232 a. Therefore, forexample, as shown in FIG. 10, the bulging body 215 can be formed of aplate-like metal material (for example, carbon steel and iron basedsintered material).

More specifically, in the bulging body 215, as shown in FIGS. 11A to 11Dand 12, a through-hole 217 b through which the holding pin 216 passesthrough is formed in a central portion of a base portion 217 a formed ina plate shape. Further, a bulging inclined surface 217 c and a circulararc surface 217 d are formed in a portion, which bulges in a directionperpendicular to the outer circumferential portion and is increased inthickness, of an outer circumferential portion of the base portion 217a. In this case, the through-hole 217 b is formed to have an innerdiameter slidable with respect to the holding pin 216, that is, adimensional tolerance which is a so-called clearance fit with respect tothe holding pin 216.

The bulging inclined surface 217 c is a flat surface which allows thepressing body 232 a of the clutch weight 230 to slide in a face contactstate. The bulging inclined surface 217 c is formed to obliquely extendrearward in the rotational drive direction of the first drive plate 210and outwardly to the first drive plate 210. The circular arc surface 217d is formed to extend in a circular arc shape from a rear end of thebulging inclined surface 217 c. The bulging inclined surface 217 c andthe circular arc surface 217 d bulge beyond a plate thickness of thebase portion 217 a and are formed to be thick. This is for easily andaccurately assembling the bulging body 215 to the supporting portion214. Therefore, the bulging inclined surface 217 c and the circular arcsurface 217 d can be formed to have the same thickness as the platethickness of the base portion 217 a.

The holding pin 216 passes through the bulging body 215 and thesupporting portion 214. At this time, the bulging inclined surface 217 cof the bulging body 215 is disposed on the supporting portion 214 in adirection of obliquely extending rearward in the rotational drivedirection of the first drive plate 210 and outwardly to the first driveplate 210. In this case, the holding pin 216 may be inserted into thebulging body 215 from below the drawing in the same manner as in theabove embodiment, or may be inserted from above the bulging body 215 inthe drawing.

As shown in FIG. 13, in the centrifugal clutch 200 configured asdescribed above, as the rotational speed of the engine increases, theclutch weight 230 is rotationally displaced toward the cylindricalsurface 241 of the clutch outer 240 while resisting the elastic force(tensile force) of the connecting spring 231. As a result, the clutchshoe 233 contacts the cylindrical surface 241. In FIGS. 12 and 13, theconnecting spring 231 is omitted in order to clarify the contact statebetween the bulging body 215 and the driven portion 232. In FIG. 13, therotational drive direction of the first drive plate 210, the seconddrive plate 220, the clutch outer 240 and the bulging body 215 in thecentrifugal clutch 200 is indicated by a dashed arrow.

When the clutch shoe 233 contacts the cylindrical surface 241, theclutch weight 230 receives a reaction force in a direction opposite tothe rotational drive direction via the clutch shoe 233. Therefore, thesecond drive plate 220 is relatively displaced in the direction oppositeto the rotational drive direction of the first drive plate 210 by thereaction force received by the clutch weight 230. Thus, the clutchweight 230 supported by the second drive plate 220 is relativelydisplaced in the direction opposite to the rotational drive direction ofthe first drive plate 210. Therefore, the pressing body 232 a of thedriven portion 232, which is in surface contact with the bulginginclined surface 217 c of the bulging body 215, is displaced along thebulging inclined surface 217 c.

In this case, the bulging inclined surface 217 c of the bulging body 215is formed to obliquely extend rearward in the rotational drive directionof the first drive plate 210 and outwardly to the first drive plate 210.Further, the pressing body 232 a of the driven portion 232 is formed onthe same plane as the bulging inclined surface 217 c and is in surfacecontact with the bulging inclined surface 217 c. Thus, as the pressingbody 232 a slides on the bulging inclined surface 217 c, the clutchweight 230 is pressed toward the clutch outer 240 on the radially outerside, and the clutch shoe 233 is pressed against the cylindrical surface241. As a result, after the clutch shoe 233 contacts the cylindricalsurface 241 of the clutch outer 240, the clutch shoe 233 is pressedagainst the cylindrical surface 241 in an extremely short time (in otherwords, instantaneously). Thus, the centrifugal clutch 200 enters theconnected state where the rotational driving force of the engine iscompletely transmitted to the drive shaft 133.

In the centrifugal clutch 200 in the connected state, since the statewhere the pressing body 232 a of the driven portion 232 is pressedagainst the bulging inclined surface 217 c of the bulging body 215 ismaintained, the first drive plate 210 and the second drive plate 220 arerotationally driven together. Further, since the state where the clutchshoe 233 is pressed against the cylindrical surface 241 of the clutchouter 240 is maintained, the second drive plate 220 and the clutch outer240 are rotationally driven together. Thus, the motorcycle vehicle canrun since the rear wheel is rotationally driven by the rotationaldriving force of the engine.

On the other hand, when the rotational speed of the engine decreases,the centrifugal clutch 200 cuts off transmission of the rotationaldriving force of the engine to the drive shaft 133. Specifically, incentrifugal clutch 200, the centrifugal force acting on the clutchweight 230 is smaller than the elastic force (tensile force) ofconnecting spring 231 as the engine speed decreases. Thus, the clutchweight 230 is rotationally displaced radially inwardly around thefulcrum pin 223.

In this case, the pressing body 232 a of the driven portion 232 of theclutch weight 230 slides on the bulging inclined surface 217 c of thebulging body 215 by the elastic force (tensile force) of the connectingspring 231. Therefore, the second drive plate 220 is rotationallydisplaced forward in a rotation direction of the first drive plate 210relatively with respect to the first drive plate 210. Thus, the seconddrive plate 220 returns to the original position (position in the idlingstate) with respect to the first drive plate 210. That is, thecentrifugal clutch 200 enters the disconnected state, where the clutchshoes 233 are not in contact with the clutch outer 240 and therotational driving force is not transmitted.

Further, in the above embodiment, the bulging body 215 is formed in aroller shape, and the pressing body 232 a is formed in a planar shape.However, it is also possible to form the bulging body 215 into a flatshape, and to form the pressing body 232 a in a rotatable roller shapeor a curved surface shape fixedly provided in a non-rotatable manner.

Further, in the above embodiment, the second drive plate 220 is formedwith the bent portion 224 bent at a right angle in each of the innercircumferential portion and the outer circumferential portion thereof.However, since the bent portion 224 is formed to increase the rigidityof the second drive plate 220, when the rigidity is secured by thematerial, thickness, or the like of the second drive plate 220, the bentportion 224 is not absolutely necessary and may be omitted. Further, thebent portion 224 may be provided on at least one of the innercircumferential portion and the outer circumferential portion of thesecond drive plate 220.

Further, in the centrifugal clutch 200 of the above embodiment, thepressing body 232 a of the driven portion 232 is made of a material moreeasily worn than the bulging body 215, specifically, a zinc material.Thus, in the centrifugal clutch 200, since the pressing body 232 a ismade of a material more easily worn than the bulging body 215, thepressing body 232 a is worn more than the bulging body 215. In thiscase, since the pressing body 232 a is formed on the clutch weight 230including the clutch shoe 233, it is renewed by replacing the clutchweight 230 due to wear of the clutch shoe 233. That is, in thecentrifugal clutch 200, by exchanging the clutch weigh 230 due to wearof the clutch shoe 233, the pressing body 232 a can also be replacedwith a new one at the same time, so that maintenance burden can bereduced.

DESCRIPTION OF REFERENCE SIGNS

-   100: Power transmission mechanism, 101: Transmission,-   110: Drive pulley, 111: Crankshaft, 112: Fixed drive plate, 112 a:    Radiating fin, 113: Movable drive plate, 114: Sleeve bearing, 115:    Roller weight, 116: Ramp plate,-   120: V-belt,-   130: Driven pulley, 131: Fixed driven plate, 132: Driven sleeve,    133: Drive shaft, 134: Movable driven plate, 135: Torque spring,-   200: Centrifugal clutch,-   210: First drive plate, 211: Bottom portion, 212: Through-hole, 213:    Cylinder portion,-   214: Supporting portion, 214 a: Through-hole, 215: Bulging body, 215    a: Through-hole,-   216: Holding pin, 217 a: Base portion, 217 b: Through-hole, 217 c:    Bulging inclined surface, 217 d: Circular arc surface,-   220: Second drive plate, 221: Ring plate, 222: Through-hole, 223:    Fulcrum pin, 224: Bent portion,-   230: Clutch weight, 231: Connecting spring, 232: Driven portion, 232    a: Pressing body,-   233: Clutch shoe,-   240: Clutch outer, 241: Cylindrical surface

The invention claimed is:
 1. A centrifugal clutch comprising: a firstdrive plate rotationally driven together with a driven pulley byreceiving a driving force of an engine; a second drive plate disposedoutside the first drive plate and contacting the first drive plate witha frictional force capable of being rotationally driven together withthe first drive plate while allowing rotational displacement relative tothe first drive plate; a clutch weight movably mounted on the seconddrive plate, displaced outwardly to the second drive plate by acentrifugal force due to rotation drive of the second drive plate, andhaving a clutch shoe on a surface outside thereof; a clutch outer havinga cylindrical surface in frictional contact with the clutch shoedisplaced outwardly to the second drive plate; a bulging body formed tobulge outwardly from an outer circumferential portion of the first driveplate; and a pressing body provided on the clutch weight and pressedagainst the bulging body, wherein at least one of the bulging body andthe pressing body is formed to extend rearwardly in a rotational drivedirection of the first drive plate and outwardly to the first driveplate; and the pressing body is constituted by a material more easilyworn than the bulging body.
 2. The centrifugal clutch according to claim1, wherein the pressing body is constituted by a flat surface, and thebulging body is constituted by a curved surface partially in contactwith the pressing body.
 3. The centrifugal clutch according to claim 1wherein at least one of an outer circumferential portion and an innercircumferential portion of the second drive plate has a bent portionbent with respect to a plate surface.
 4. The centrifugal clutchaccording to claim 1 wherein at least one of two contact surfaces wherethe first drive plate and the second drive plate are in contact witheach other is subjected to surface treatment to maintain slidability.